1. Field of the Invention
The present invention relates to a planetary gear type multistage transmission.
2. Description of the Prior Art
Japanese Patent First Provisional Publication No. 63-303245 shows a conventional planetary gear type transmission with five forward speeds, which comprises generally a single pinion type planetary gearset, a double pinion type planetary gearset, four clutches, five brakes and four one-way clutches.
However, due to its inherent construction, the transmission has the following drawbacks.
That is, when the transmission intends to achieve a speed change from first speed to second speed, a switching from one clutch to another clutch and a switching from one one-way clutch to another one-way clutch must be carried out at substantially same time. However, these switchings tend to produce undesirable shift shock for the reason which will be described in the following.
For ease of understanding, the description will be made with reference to FIG. 13 of the attached drawings, which shows schematically the conventional transmission of the publication.
For achieving the speed change from first to second speed, four friction elements are subjected to switching operation (viz., "ON to OFF" operation or "OFF to ON" operation). That is, for achieving such speed change, disengagement (viz., "ON to OFF" operation) of second clutch C2, engagement (viz., "OFF to ON" operation) of third clutch C3, disengagement (viz., "ON to OFF" operation) of fourth one-way clutch F4 and engagement (viz., "OFF to ON" operation) of second one-way clutch F2 are necessary.
However, if the switching from the second clutch C2 to the third clutch C3 is carried out prior to that from the fourth one-way clutch F4 to the second one-way clutch F2, there is inevitably produced a temporary condition wherein parts connected to an input shaft are interlocked and parts connected to an output shaft are neutral. While, if the switching from the fourth one-way clutch F4 to the second one-way clutch F2 is carried out prior to that from the second clutch C2 to the third clutch C3, the parts of the transmission assume but temporarily a reverse condition.
As will be understood from the above, when, in the transmission of the publication, engagement and disengagement of selected two of four friction elements (viz., four in a group including the four clutches C1 to C4, the five brakes B1 to B5 and the four one-way clutches F1 to F4) are carried out prior to those of the remaining two, interlocked condition, neutral condition and reversed condition tend to occur temporarily in the transmission. As is known, these conditions cause an undesirable shift shock during the speed change.
Accordingly, in the transmission of this type, it is quite important to adjust the engaging and/or disengaging timings of the four friction elements to optimal levels. In fact, if, for achieving a desired timing in switching from the second clutch C2 to the third clutch C3, the disengaging timing of the second clutch C2 is changed, this change has effect on not only the third clutch C3 but also the other friction elements. Thus, the adjustment of the timing is quite difficult.
Although the difficulty in such timing adjustment is somewhat lightened by use of the one-way clutches F1 to F4, the timing adjustment of the one-way clutches is somewhat difficult as compared with that of the switching from one clutch to another clutch or that of switching from one brake to another brake.
Besides the above-mentioned drawbacks, the conventional transmission of the publication has further the following drawbacks.
That is, because the part's layout does not permit the transmission to have an output shaft which extends in a direction opposite to the direction in which an input shaft extends, a so-called "longitudinally mounted transmission" (viz., a transmission for "FR type" motor vehicle) is not expected from such transmission.
Furthermore, usage of the four clutches C1 to C4, the five brakes B1 to B5 and the four one-way clutches F1 to F4 induces a bulky construction of the transmission.